1. Field of the Invention
The present invention relates to the storage of data on hard disk drives, and more specifically relates to methods of dealing with bad portions of the disk.
2. Background of the Related Art
Data storage is a fundamental function of any computer system. The various types of data storage devices each have their own role and may find a specialized role that takes advantage of their strengths while minimizing their weaknesses. For example, hard disk drives are good at storing large amounts of data and, because they are non-volatile, they can store data without continual application of electricity. However, hard disk drives are also much slower than RAM, flash or cache memory, so any given computer system is unlikely to rely solely on a hard disk drive.
Still, hard disk drives are used in most notebook computers, desktop computers, servers, redundant arrays of independent disks (RAID) systems, storage area networks, and datacenters. These hard disk drives are responsible for storing operating systems, applications, and files and data of all types. The reliable operation of the hard disk drives is imperative to the operation of the computer systems that use those hard disk drives.
A hard disk drive includes one or more rotating disc-shaped platters and magnetic heads arranged on a moving actuator arm to read and write data to the surfaces of the platters. Unfortunately, the surface of a platter may become scratched or develop a crack, thereby making one or more block or sector of the platter unusable. Such a damaged area of a platter may be referred to as “failed” or “bad”, and the blocks that are associated with the damaged area may be referred to as “failed blocks” or “bad blocks.” Data previously stored in a failed block is likely to be corrupted or unreadable, and data may no longer be reliably written to the failed block.